Remote emissions sensing (RES) systems are known. Such systems are generally utilized for remotely monitoring the exhaust gas composition of motor vehicles. Examples of RES systems and methods are described in, for example, U.S. Pat. Nos. 5,210,702, 5,319,199, 5,401,967, 5,591,975, 5,726,450, 5,797,682, and 5,831,267, each of which is hereby incorporated herein by reference in its entirety.
Despite steady advances in their sophistication and robustness, the manufacture and/or calibration of some instruments (e.g., detectors or detector arrays) utilized in RES systems may suffer from various drawbacks. For instance, one drawback associated with instrument manufacture is the need to separately calibrate each detector channel with known column densities of relevant pollutant gases.
Additionally, when remotely monitoring the exhaust gas composition of motor vehicles on a roadway or driving surface under various operating conditions, it may be expensive and/or inconvenient to have to repeatedly recalibrate on-road instruments using expensive, certified gas cylinders of surrogate exhaust pollutants. Such recalibration may be necessary for conventional instruments to compensate for changes in background (or ambient) CO and CO2 concentrations over time. CO2, for example, is reasonably abundant in the atmospheric optical path used for measurement, and may vary with wind speed, wind direction, and traffic volume, among other factors. These and other drawbacks exist with known calibration methods.